1. Technical Field
The present invention relates to a zirconium oxalate sol.
2. Description of Related Art
A photocatalyst is a catalyst which exhibits an activity upon irradiation with light and is coated to a base material, together with a binder component, and used as a coat as disclosed in PCT International Publication No. WO98/15600, Japanese Patent Application Laid-Open No. 2003-105262, Japanese Patent Application Laid-Open No. 9-328336 (1997), Japanese Patent Application Laid-Open No. 2004-59686, PCT International Publication No. WO01/023483, Japanese Patent Application Laid-Open No. 11-209691 (1999) and PCT International Publication No. WO99/028393.
However, a coat formed from a conventional photocatalyst coating liquid has not necessarily a sufficient adhesion strength to a base material, and therefore it was necessary to increase a use amount of a binder component with respect to a photocatalyst in the coating liquid. When a large amount of the binder component is used, it becomes difficult for the photocatalyst to sufficiently exhibit the activity.
When a sol containing fine particles of a metal compound as a dispersoid is used as a binder, since the sol is excellent in dispersibility, it is easy to uniformly mix with a photocatalyst. Therefore, it can be expected that a structure of a film can be made uniform and strong binder ability is exhibited, and thus a coat of a photocatalyst with good quality is formed.
Among fine particles of the metal compound, fine zirconium compound particles have a property in which Zr atoms are easily polymerized via an OH group, and therefore it is considered that fine zirconium compound particles have high suitability for use as a binder of a photocatalyst coating liquid. A sol of a zirconium compound which is considered to have high suitability for use as a binder of a photocatalyst includes, for example, a sol disclosed in Japanese Patent Application Laid-Open No. 2007-70212, namely, a sol containing amorphous Zr—O-based particles having an average particle diameter of 10 nm as a dispersoid, the sol (pH 3.2) containing 0.4 gram equivalents of nitric acid with respect to 1 mol of Zr. It can be expected that this sol comprising Zr—O-based particles as a dispersoid has high suitability for use as a binder of a photocatalyst coating liquid since the dispersoid is amorphous and has an average particle diameter of 10 nm.